Conventional warewashing detergents are normally phosphate-based, highly alkaline compositions comprising a chlorine bleach. However, the high alkalinity and the chlorine bleach have proved to be too aggressive and hazardous for common use. Further, the use of phosphate and phosphorus containing compounds is discouraged due to environmental concerns. There is therefore a growing interest to replace these compositions with less alkaline compositions, which do not contain phosphate and which use a milder bleach instead of chlorine bleach.
It is known in the art to replace chlorine bleach with milder peroxide bleaches such as sodium perborate or sodium percarbonate. To compensate the reduced performance of said bleaches, an organic activator or bleach precursor can be added, which reacts with the perborate or percarbonate to form an organic peroxyacid. A well-known bleach activator is N,N,N′,N′-tetraacetylethylenediamine (TAED).
To further increase the performance of warewashing compositions, U.S. Pat. No. 5,246,612 has suggested to use a dinuclear manganese complex in combination with a peroxygen compound.
The combination of a manganese complex as bleach catalyst and a peroxygen compound has also been disclosed in the context of a laundry detergent bleach powder composition in EP 0 509 787 A2.
As an alternative for the highly alkaline detergent compositions, mild alkaline detergent materials have been developed on the basis of sodium carbonate as a source of alkalinity (see for example U.S. Pat. No. 7,094,746 B2). These compositions provide mechanically stable solid carbonate detergent products having equivalent cleaning performance when compared to caustic based detergents, but are considerably less alkaline.
Against this background there is still the need to develop further warewashing detergents specifically tailored towards institutional warewashing applications. One of the key objectives here is to deal with coffee and tea stains as well as with starch soil.
The technical object of the present invention therefore is to provide a warewashing detergent composition that is not phosphate-based, of mild alkalinity, and is highly effective for the removal of starch soil.
It has surprisingly been found that a composition comprising an alkali metal carbonate as a source of alkalinity, an alkali metal percarbonate as a peroxygen bleach compound, and an iron or manganese complex as peroxidation catalyst provides a highly efficient warewashing detergent for the removal of starch soil.